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Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Assessment Program.

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Tributyltin

Publication Date: 9/93

INTRODUCTION

Tributyltin (TBT) is the active ingredient of many products that act as
biocides against a broad range of organisms. It is primarily used as an
antifoulant paint additive on ship and boat hulls, docks, fishnets, and buoys
to discourage the growth of marine organisms such as barnacles, bacteria,
tubeworms, mussels and algae

TBT by itself is unstable and will break down in the environment unless
it is combined with an element such as oxygen. One of the most common TBT
compounds is bis(tributyltin) oxide, or TBTO. This form has been the subject
of most TBT testing.

TBTO and eight additional TBT compounds are registered for use as marine
antifoulants. Other TBT compounds are used as disinfectants, fungicidal wood
preservatives, textile disinfectants, and stabilizers in PVC resin. Paper and
pulp mills, cooling towers, breweries, textile mills and leather-processing
facilities may also use some forms of TBT. Collectively these compounds are
refered to as organotins.

All of the organotins are now regulated by the "Organotin Antifouling
Paint Control Act of 1988." This act regulates the use of these materials in
paints and sets standards for the amount of biocides that can leach from the
paint into water.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

TBT is moderately to slightly toxic to mammals. Human skin is sensitive
to TBTO, although the extent of sensitivity is not known. TBT can cause eye
irritation in humans exposed over a few hours (5). Inhalation of TBT may
interfere with breathing and cause headache, weakness, tremors and
incoordination. The lowest concentration inhaled from the air that causes
toxicity in humans is 10 ppm for three minutes and 20 ppm for five minutes
(5). The oral LD50 of TBT is 1,500 mg/kg for rats, 2,000 mg/kg for rabbits,
and 900 mg/kg for mice (5). The dermal LD50 of TBTO is 11,700 mg/kg for rats
and 900 mg/kg for rabbits (7). Two products containing TBT, Triphenyltin
hydroxide and triphenyl chloride both carry the signal word WARNING.

CHRONIC TOXICITY

Studies of the effects of TBT products on living organisms have been
primarily performed on aquatic life, because TBT is mostly used in bodies of
water. Thus, data gaps exist concerning effects of TBT on mammals in regard
to reproduction, development and mutagenicity. Although effects of TBT on
humans is not clear, several incidents of human exposure to the biocide have
been reported. Underwear treated with TBT has caused severe skin irritation
to its wearers. Shipyard workers exposed to TBT dust and vapors, while
repairing a submarine, developed breathing problems, irritated skin,
headaches, colds, flu, fatigue, dizziness and stomach aches (1). TBT exposure
can also irritate the eye, skin, and mucous membranes and prolonged exposure
may cause liver and kidney damage (5).

Carcinogenic Effects

While one study indicates that rats have developed pituitary gland tumors
after exposure to high doses of TBT, the evidence is not conclusive (1) and
the carcinogenic status of TBT is still uncertain (5).

Organ Toxicity

In mammals, high levels of TBTO can affect the endocrine glands,
upsetting the hormone levels in the pituitary, gonad and thyroid glands. Large
doses of TBT have been shown to damage the reproductive and central nervous
systems, bone structure, and the gastrointestinal tract of mammals.

Fate in Humans and Animals

In mice, TBTO is excreted mainly unchanged via the feces, indicating low
absorption by the body. An undetermined amount of this compound is known to
remain in fat, liver, kidney, and lung tissues. The makers of TBT, M & T
Chemicals, claim that workers exposed to this substance metabolize it within
three days (2).

ECOLOGICAL EFFECTS

Much of the concern over the use of tributyltin stems from its use as a
marine antifoulent in paints. This compound is slowly released from the paint
on the hull of the boat into the adjoining water hindering the growth and
attachment of a variety of organisms to the boat. Consequently, tributyltin
concentrations in harbors and bays in Britain, France and the United States
were high enough to significantly affect oyster and mussel production.

TBT is extremely toxic to crustaceans. Lobster larvae show a nearly
complete decrease in growth at just 1.0 ppb TBT (1). Molluscs, used as
indicators of TBT pollution because of their high sensitivity to these
chemicals, react adversely to very low levels of TBT (0.06-2.3 ppb). They
release TBT very slowly from their bodies after it has been absorbed.

TBT toxicity in the field may be substantially underestimated in
laboratory studies (1). TBT binds to the sides of containers and plankton
which contributes to this underestimation of it's potential toxicity.
Generally, the larvae of any tested species are more sensitive to tributyltin
exposure than are the adults.

The present use of TBT in antifouling paints may cause TBT exposure to
nontarget aquatic organisms such as mussels, clams, and oysters. At low
levels, TBT can cause structural changes and growth retardation (3).

Imposex, the development of male characteristics in females, has been
initiated by TBT exposure in several snail species. In laboratory tests,
reproduction was inhibited when female snails exposed to 50 ppt of TBT
developed male characteristics (1). Imposex was also noted in the mud snail,
or dogwhelk, at less than 3 ppt TBT (1).

Some fin fish can degrade TBT because of special enzymes these fish
contain. Once absorbed in Chinook salmon, TBT breaks down into di-n-butyltin
(DBT). Rainbow trout eggs are killed within 10-12 days when exposed to 5 ppb
TBT. At lower levels, no deaths occurred, but blood and liver metabolism
changes were noticed (6). Growth reduction and liver changes also occurred in
young trout exposed to low levels of tributyltin chloride. Also, after seven
days at low levels of TBTO, the corneal membranes of the rainbow trouts' eyes
were destroyed (1).

TBTO has been shown to inhibit cell survival of marine unicellular algae
at very low concentrations; the 72-hour EC50 ranges from 0.33 ppb to 1.03 ppb
(1).

TBT is highly attracted to fats and tends to be stored in these tissues.
TBT is accumulated in oysters, mussels, crustaceans, molluscs, fish, and
algae. Freshwater species will bio-accumulate more TBT than will marine
organisms.

Evidence of organotins entering the human diet has been observed with
Chinook salmon, which may be commercially raised in TBT-treated pens.
Juvenile chinook salmon accumulate TBT immediately upon exposure to low TBT
concentrations. TBT and its metabolite, DBT, were found in the salmon's
muscle tissue (8).

ENVIRONMENTAL FATE

Degradation depends on temperature and the presence of microorganisms.
The breakdown of TBT leads eventually to the tin ion. All of the breakdown
products are less toxic than TBT itself.

Under aerobic conditions, tributyltin takes one to three months to
degrade. But in anaerobic (airless) soils, this compound will persist for
more than two years.

Because of the low water solubility (inability to dissolve in water) of
TBT and other properties, it will bind strongly to suspended material such as
minute organic material or inorganic sediments (4). The extent of binding to
bottom sediment will vary with location, organic content, particle size, and
type of material.

The half-life of TBT in water is about three months. Also, the chemical
nature of TBT compounds generally keeps them within the water areas where they
were applied.

Levels up to 800 ppt have been found along the East Coast of the United
States. In the Great Lakes, concentrations from 20 to 840 ppt have been
recorded. San Diego Bay has reached 1,000 ppt TBT (11).

It has not been found in groundwater.

COMMENTS AND PROBLEMS

U.S. law now restricts the use of TBT on non-aluminum boats shorter than
65 feet.

Two kinds of TBT-containing paints are known. Free-association paint,
made by mixing TBT into the paint, dissolves when it contacts water. All of
the TBT is leached out from the paint in 12-24 months. In copolymer paint,
the TBT is bound to the paint and slowly releases with water movement, and is
effective for five to six years.

The EPA has established a cut-off release rate of 4.0 ug/cm2/day as
sufficient to keep a ship's hull free of fouling, while causing minimal risk
to aquatic mammals.

PHYSICAL PROPERTIES AND GUIDELINES

Tributyltin is a member of the aromatic hydrocarbon chemical family. It is a
colorless liquid with an odor similar to gasoline. The molecular weight of
TBT is 148.25. One of its metabolites, bis-(tri-n-butyltin) oxide (TBTO) is a
slightly yellow, combustible liquid.

Hugget, R.J. September 30, 1986. "Tributyltin Based Antifouling
Paints -- Environmental Issues." Testimony before the Subcommittee on
Oversight and Investigations of the House of Representatives Committee on
Merchant Marine and Fisheries.